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Constrained circle in quadrilateral (Posted on 2021-04-09) Difficulty: 2 of 5
A circle is contained in a quadrilateral with successive sides of lengths 3,6,5 and 8. Prove that the length of its radius is less than 3.

No Solution Yet Submitted by Danish Ahmed Khan    
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re: Solution? Comment 2 of 2 |
(In reply to Solution? by tomarken)

I agree, the max diameter seems it must be under 5.


The quadrilateral has only 1 degree of freedom so its easy to draw in Geometer's Sketchpad (or Geogebra)

The maximum radius of the circle is about 2.105 where the circle touches all but the shortest side.

Where the angles (starting where 3 and 6 meet) are
77.26
120.25
91.35
71.14 

  Posted by Jer on 2021-04-10 11:07:11
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